1. Field of the Invention
This invention relates to a process of recovering oil from oil-containing minerals wherein the oil-containing mineral is charged onto a traveling grate, hot gases are passed through the bed in a retorting zone to heat the bed to the retorting temperature, the vaporous and gaseous retorting products are entrained by the retort gases, oil is separated from the retort gases in a separating stage, solid carbon in the retorted bed is burnt in a succeeding combustion zone by means of oxygen-containing gases passed through, gases from which oil has been removedin the separating zone are passed through the bed in a succeeding cooling zone, and the heated gases are recycled to the retorting zone.
2. Discussion of Prior Art
Oil-containing materials, such as oil sand, diatomaceous earth and particularly oil shale are heat-treated on traveling grates to recover their oil content. In the retorting zone, hot gases are passed through the bed to heat the latter to the retorting temperature of about 400.degree. to 600.degree. C. The hot gases are neutral or reducing gases so that the retorting is effected in the absence of oxygen. During the retorting various gases and vapors are formed from the organic constituents. The oils are condensed from the retort gases. After the condensation, the gas still contains gaseous retorting products which cannot be condensed. The retorted residue on the traveling grate contains solid carbon as a retorting product. For the sake of heat economy, that carbon must be burnt and the resulting heat must be utilized for the process.
It is known from U.S. Pat. No. 3,325,395 to pass hot non-oxidizing gases through the bed in a first zone of the traveling grate so as to effect retorting in said first zone only in the upper portion of the bed and to pass air through the bed in a second zone, so as to burn the solid carbon formed in the upper portion of the bed and to use the resulting hot gases to effect retorting in the lower portion of the bed. After the oils have been condensed, thegas is passed through thebed from below in the cooling zone and is thus heated and after a combustion of combustible constituents effected with a supply of air is recycled to the first retorting zone. A partial stream is branched from the gases leaving the cooling zone.
The combustion of the non-condensible constituents in the recycled gas stream decreases the heating value of the retort gases which have passed through the retorting zone and left the separating stage, because the percentage of the non-condensible combustible constituents is low. Additionally, part of the non-condensible constituents in the exhaust gas is lost. The non-condensible constituents formed in the second retorting zone are lost or form also a lean gas. In addition, an expensive control is required in order to maintain non-oxidizing conditions in the combustion zone for the solid fuel and it is hardly possible to maintain such non-oxidizing conditions.
It is known from U.S. Pat. No. 3,644,193 to conduct the gases from below through the bed in a first zone so as to preheat the bed to a temperature below the retorting temperature and to cool the gases, which are subsequently fed to a mechanical separating stage for a separation of the oils. Hot gases are passed through the bed in a second zone to effect retorting. Hot air is passed through a third zone to burn the solid carbon. The hot gases from the combustion zone are conducted in a round traveling grate through a bed of heat exchange bodies and heat the latter. The gas from the separating stage is passed through the heated heat exchange bodies and is thus heated and then recycled to the retorting stage. A partial stream of the gas from the separating stage is burnt and admixed to the gases from the combustion zone. The repeated separation of oil decreases the yield. The heat exchange with the aid of heat exchange particles is expensive and causes heat losses. The heat exchange bodies are spoiled by dust and must be cleaned.
It is known from U.S. Pat. No. 4,039,427 to effect a retorting and a subsequent cooling o a first traveling grate and a combustion of the solid carbon and of residual hydrocarbons on a second traveling grate. The retort gas from which the oil has been removed is forced through the cooling zone and is thus heated. One partial stream is discharged and another partial stream is passed through the hot bed of the second traveling grate and is further heated there and then fed to the retorting zone. Two traveling grates are required. The transfer of material from one traveling grate to the other involves heat losses, the heat loss due to the cooling on the first traveling grate must be compensated by a corresponding supply of energy on the second traveling gate, and the gas which leaves the cooling zone of the first traveling grate and contains non-condensible constituents is uselessly heated.
It is also known from U.S. Pat. no. 4,082,645 to effect retorting in the retorting zone only in the upper portion of the bed and to effect retorting in the combustion zone in the lower portion of the bed. Oxygen is passed through the bed at controlled rates. As the gases from all retorting zones and from the cooling zone are combined, only a lean gas becomes available when the oil has been separated. Besides, the previously described problems arise as regards the control of the oxygen content in the retorting zone.
It is known from U.S. Pat. No. 4,193,862 to suck oxygen-containing gases that contain 5 to 15% water through the bed behind a retorting zone in order to burn the solid carbon. After the separation of oil, the gases from the retorting zone are passed through the cooling zone and then recycled to the retorting zone. A partial stream is discharged from the end of the cooling zone. The dissociation of the water content in the combustion zone is an endothermic reaction, by which heat is consumed. For this reason the process can be used only if the content of solid carbon is sufficient so that there will be an overall heat surplus in the process. Additionally, when the oil has been separated a lean gas will be obtained and that partial current thereof which is discharged has been uselessly heated.
It is an object of the invention to avoid the disadvantages which have been described and particularly to permit a retorting and combustion with a minimum of expenditure for processing and control equipment and to recover as much oil and energy from the minerals supplied.